Container

ABSTRACT

A cylindrical metal can body for pressurized products having integral side and bottom walls is constructed such that the bottom wall includes a centrally disposed circular depression or dimple therein, the base area of the depression being less than approximately 60 percent and greater than approximately 15 percent of the total area of the bottom wall. This bottom wall structure permits the can to expand in height when subjected to internal pressure, while preserving stability when placed in an upright standing position since the bottom is uniformly deformed by the internal pressure into a shape in which the circular rim of the depression forms a suitable stable base on which the can sits.

United States Patent 191 Toukmanian 1 CONTAINER Aram Hartoun Toukmanian,Downsview, Canada {75] Inventor:

American Can Company, Greenwich, Conn,

[22] Filed: Oct. 25, 1973 [21] Appl No; 409,734

Related US. Application Data [63] Continuation-impart of Ser, No,222,050, Jan. 31,

1972, abandoned.

[73] Assignee:

1 1 Sept. 9, 1975 Primary Emminer-George E. Lowrance Asrr'slanrExaminer-Allan N. Shoap Attorney, Agent, or Firm-Robert Pl Auber; JamesW. Bock; George P. Ziehmer 5 7 ABSTRACT A cylindrical metal can body forpressurized products having integral side and bottom walls isconstructed such that the bottom wall includes a centrally disposedcircular depression or dimple therein, the base area of the depressionbeing less than approximately 60 percent and greater than approximately15 percent of the total area of the bottom wall. This bottom wallstructure permits the can to expand in height when subjected to internalpressure, while preserving stability when placed in an upright standingposition since the bottom is uniformly deformed by the internal pressureinto a shape in which the circular rim of the depression forms asuitable stable base on which the can sits.

30 Claims, 21 Drawing Figures PATENTEDSEP 91975 3, 904,069

SHEET 1 FIG. 3 FIG. 4

PRIOR ART SHEET PATENTEU 975 FIG.8

FIG. 7

FIG. IO

FIG.9

FIG.

FIG.|2

PATENTEB SEP 9I975 3,904,069

SHEET us STEEL 0.050

I I O 20 4O 6O 80 I00 I20 Inferno! Pressure PSI G FIG-I5 Con HeightGrowfh Inches) PATENTEDSEP' 9:975 3.904.069

SHEET 4 Foiled- |o3 STEEL I I I T 60 Internal Pressure PSIG Fl 6 I4 ConHeight Growth (Inches) PATENTEDSEP 9M5 3.904.069

SHEET .Ol4 ALUMINUM Internal Pressure PSIG FIG I6 PATENTEU SEP 9 I915FIG-l8 ||8 STEEL O O O O O 5 4 3 2 235m I mma QE E @965 InternalPressure -PSIG PATENTED SE? 9 I975 Change in Dimple DepIh- Percent sum 9F I G. I9

|03 STEEL O v 1 l I I I o 20 40 e0 80 I00 I20 Internal Pressure-PSIGChange in Dimple Depth Percent SHEEI 1 1 FIG.2|

.OI4 ALUMINUM A l T I 40 6O 80 Internal Pressure PSIG I I00 I20 1CONTAINER This application is a continuationin-part of my applicationSer. No. 222,050, filed Jan. 31. 1972, now abandoned.

The present invention relates generally to an improved can or containerconstruction which enhances the ability of the container to maintain anupright standing position when the container is subjected to internalpressure. More particularly. the present invention relates to animproved bottom wall construction for a container, in which the side andbottom walls of the container body are integrally formed, such that whenthe container is subjected to internal pressure the bottom wall isdeformed in a uniform and predictable manner to provide a suitable baseupon which to uprightly position the container.

At the present time conventional metallic containers may be formed fromeither two or three pieces of metallic material. In the three-piececontainer the components include a container body, which may becylindrical in shape, and two suitable end closures secured to the endsof the container body. The components of the two-piece container includea container body having integral side and bottom walls and a separateend closure for closing the one open end of the container body. Thetwopiece container. being the type container with which the presentinvention is primarily concerned, presents numerous advantages over theconventional three piece container with respect to manufacturing easeand aesthetic appeal. The container body of the two-piece container ofthe present invention is preferably made by drawing and ironing sheetmetal and must. therefore. generally be constructed from a relativelyductile material. Drawing and ironing is a known can body formingprocess in which a sheet metal blank is first drawn into a relativelyshal low cup and then the walls of the cup are ironed, which is to saythinned and extended to a height appropriate for the can. The bottomremains approximately as thick as the starting sheet. U.S. Pat. Nos.2,412.8 l3, 3,203,218 and 3,360,157 describe this process. If thecontainer is made with a flat bottom wall, the internal pressuresencountered with pressurized products such as beer or carbonatedbeverages cause the bottom wall of the container to deform outwardlyinto a convex configuration making it unstable when stored in an uprightposition unless the strength of the bottom wall is increased towithstand the pressure. Increasing the thickness of the starting sheetwill provide a stronger bottom. but at the cost of more metal and highershipping weights.

In order to increase the strength of bottom walls of container bodieshaving integral side and bottom walls, to thereby better withstand thepressures created by beer and carbonated beverages. it is well known toform the bottom wall of the container as an inwardly concave dome ordepression which extends substantially throughout the bottom wall ofthecontainer. The increased strength provided by this fully domed bottomwall construction resists deformation of the bottom wall under increasedinternal pressure of the container with little change in theconfiguration of the bottom wall throughout the pressure range for whichthe container is designed. The container rests on the rim of the domeadjacent the cylindrical wall. A disadvantage of this fully domedconstruction is that upon elevation of the pressure beyond a criticalpoint. the bottom wall of the container suddenly pops out or everts.This is a catastrophic failure since the container suddenly becomesunserviceable due to its now swollen shape. In order to prevent suchfailure. the thickness of the bottom wall of the container must besufficient to safely satisfy not only the pressure conditionsanticipated, but also, because of the catastrophic nature of theeversion, must be able to resist pressures in excess of anticipatednormal pressures, Another disadvantage of the full concave bottom wallconstruction is the difficulty of washing and protectively coating theinterior of the container due to the high angle of the depression, whichis in the nature of a countersink. Since the containers are washed andspray coated from their open ends, the bottom walls require a great dealof effort to be properly washed and coated. A still further disadvantageof the full concave bottom wall construction is the internal volume lostby virtue of the intrusion of the dome. More metal must be used to makethe container large enough for its design capacity.

It is. therefore, an object of the present invention to provide a metalcontainer having integral side and bottom walls wherein an improvedbottom wall construction reduces or eliminates catastrophic eversionfailure of the bottom wall, permits rather than resists expansion of thecontainer under internal pressure while maintaining a stable support.and wherein minimum metal is required for a particular internal volumeand for sufficient strength to safely withstand anticipated internalpressures.

The cylindrical container of the present invention is constructed withthe integral bottom wall including a substantially flat panel sectionhaving a centrally disposed circular depression or dimple therein, thebase area of the depression being no greater than approximately 60percent and no less than approximately 15 percent of the total area ofthe bottom wall. This bottom wall construction provides a stablesupporting base for the container when the container is subjected tointernal pressure since the bottom is uniformly deformed by the internalpressure into a shape having a uniform circular ring upon which thecontainer rests.

The present invention will be described and understood more readily whenconsidered together with the accompanying drawings; in which;

FIG. I is a perspective view of the container body of the presentinvention shown in longitudinal section;

FIG. 2 is a perspective view of a slightly modified form of thecontainer body of the present invention shown in longitudinal section;

FIG. 3 is a,,,c r0ss-sectional view of the lower portion of a prior artcontainer body;

FIG. 4 is a cross-sectional view of the lower portion of another priorart container body;

FIG. 5 is an enlarged, cross-sectional detailed view of the lowerportion of the container body of FIG. 1;

FIG. 6 is an enlarged, cross-sectional detailed view of the lowerportion of the container body of FIG. 2;

FIGS. 7 through ll are enlarged, cross-sectional detailed views of thelower portion of the container body of FIG. 1 showing the deformation ofthe bottom wall as the container is subjected to increasing internalpressures;

FIG. 12 is an enlarged cross-sectional detailed view of the lowerportion of a container body of the present invention illustrating themanner of measurement of the ratio of the area of the depression to thetotal area of the bottom;

FIGS. 13-16 are graphic displays of data for different startingmaterials showing can height growth as a function of internal pressurefor various depression sizes for containers according to the presentinvention,

FIG. I7 is a graphic display of data showing the stability of cansaccording to the present invention as a function of the size of thedepression; and

FIGS. l82l are graphic displays of data for different starting materialsshowing percentage change in depression or dimple depth as a function ofinternal pressure for various depression sizes for containers accordingto the present invention.

Now referring to the drawings, there is shown in FIG. 1 a containerbody, generally designated 20, which has been sectioned in half in orderto better demonstrate the present invention. The container body includesa side wall 22 and a bottom wall 24 which are integrally formed. Thistype of container body, having integral side and bottom walls, ispreferably formed of any suitable metallic material such as steel oraluminum by the known process of drawing and ironing.

As is shown in FIGS. 1 and 5, the bottom wall 24 of container body 20has a substantially flat annular panel section, generally designated 26,having a centrally disposed circular depression or dimple 28 formedtherein. The depression 28 may be of almost any suitable shape providedthat the base edge or marginal intersection 30 of the depression withthe annular panel 26 is circular so that the annular panel section 26surrounds the depression. Although the depression 28 is shown in thedrawings as having the shape of a segment of a sphere it may also be inthe shape ofa truncated cone, an ellipsoidal segment or a paraboloidalsegment. At the periphery of the annular panel section 26 of FIGS. 1 andthere is provided a 45 angled transition edge, designated 32, integrallyinterconnecting bottom wall 24 to side wall 22.

As is shown in FIGS. 2 and 6., which show a slightly modified form ofthe present invention, the 45 angled transition edge 32 is replaced by aradiused transition edge, designated 32a. The open end of container isprovided with a substantially horizontal flange, generally designated34, for the purpose of seaming an end closure (not shown) to the upperextremity of side wall Prior two-piece containers for pressurizedproducts such as beer or carbonated beverages have inwardly domedbottoms which extend to the cylindrical side walls. Many of thosemarketed employ a transition between the rim of the dome and thesidewall which usually is in the form of a radius which forms a rim onwhich the can sits. FIG. 3 is a depiction (not to scale) of one variantof this general construction in which the sidewalls 1 l2 are turnedinwardly toward the bottom to form a chamfered transition 4 which thenmerges with a radius 118 which forms the rim upon which the can sits.The dome l 16 extends from rim 118 across the bottom 110 of the can.FIG. 4 is a depiction (not to scale) of a proposed construction shown inFIGS. 2 and 3 of U.S. Pat. No. 3,272,383 to Harvey. To more closelyresemble a three-piece can for handling purposes, the proposed Harveyimpact extruded two-piece can is provided with a bead 155 having thcapproximate external size and shape of the bottom chine of aconventional three-piece can. The bottom I52 extends beyond thecylindrical wall of the can to accommodate the bead 155. Between thebead 155 and the inward 4 dome is an annular margin 154 for supportingthe container.

None of these prior bottom constructions is intended to expand in heightin response to internal pressures. All are intended to resist expansionby confining the rim of the dome by the adjacent side walls or, inaddition, by the thick walls and bottoms inherent in containers made byimpact extrusion. The large domes of these prior art constructions areprone to sudden catastrophic eversion or pop-out when the internalpressure exceeds the structural strength of the bottom wall. Theconstruction of the present invention avoids this catastrophic failuresince the container of the present invention expands in a gradualpredictable manner without eversion and continues to provide a stablesupport base throughout the pressure range for which it is designed andbeyond.

FIGS. 7 through II demonstrate five stages in the continuous deformationthrough which the bottom wall 24 of a container body according to thepresent invention passes when subjected to increasing pressures.Throughout the stages depicted, the dimple or depression 28 remainsconcave in the inward direction thereby providing a suitable supportbase at the marginal circular intersection or edge 30 on which thecontainer rests. The first stage, which is represented in FIG. 7,depicts the configuration of the bottom wall 24 when the container issubjected to no pressure, the configuration in this figure is identicalto that shown in FIG. 5. The second stage, shown in FIG. 8, depicts theconfiguration of the bottom wall when the container is subjected to anincreased pressure over that of FIG. 7. The height of the depression 28in this second stage is slightly reduced or flattened and annular panelsection 26 is slightly angled downwardly due to the applied pressurewhich causes the development of horizontal, outwardly directed forcesnear the edge 30 of the depression 28. The deformation in this stage isstill in the elastic range and therefore, the bottom wall 24 will returnto its original shape as the pressure is released. The third stage isdepicted in FIG. 9 wherein the pressure is increased over that of thesecond stage and where the material no longer remains in the elasticrange. As can be readily seen, the height of the depression 28 isfurther reduced. FIG. 10 depicts the fourth stage through which thebottom wall 24 passes when subjected to a further increased pressureover that of the third stage. As can be seen, the panel section 26 andthe angled transition edge 32 are deformed outwardly even further inthis stage. In addition, the height of the depression 28 is furtherreduced as a result of the increased pressure. The fifth stage isdepicted in FIG. 11 where the increased pressure further reduces theheight of depression 28. At this stage, there is a gradual andcontrolled further flattening of the depression 28 and the radius ofintersection of edge 30 unrolls. This multiple stage controlledexpansion is to be contrasted with the non-expansion followed byirregular bulging and catastrophic eversion encountered with the largedomes of the prior art.

Proper selection of angle A (FIG. 7) the acute angle of the intersectionof the annular panel 26 with the immediately adjacent portion ofdepression 28 will delay the deformation ofstage four. depicted in FIG.10, until a more elevated pressure is reached. However, this will notprcvcnt the occurrence of deflection of the annular panel section 26into a generally conical shape as depictcd in FIGS. 9 through II. Thegreater angle A is.

the greater the resistance to outward expansion of bottom wall 24. Ithas been found that angle A should be no less than about 43". In orderfor the depression 28 to be formed with conventional dies, angle Ashould be made no greater than 90 and preferably about 60 in order toproperly wash and spray coat the bottom wall of the container body.

Cans used for the packaging of pressurized products such as beer orcarbonated beverages must be able to withstand internal pressures ofabout 95 psig. Beer is usually pasteurized in the filled and sealed canat a temperature and for a time which results in an internal pressure of85 psig. To allow for errors of temperature or time, the minimumacceptable pressure capacity is 90 psig. Carbonated beverages varyaccording to the degree of carbonation. The highest degree ofcarbonation is encountered with club soda water which may produce aninternal pressure at 100F of approximately 95 psig. Since the same canbody should be useful for all pressurized beverages, 95 psig is taken tobe the minimum pressure capability.

Unlike the previous pressurized beverage containers. the construction ofthe container of the present invention is intended to expand in heightas a result of internal pressure. When shipped from the beverage maker,filled cans according to the present invention are expanded from theirunfilled configuration. Should the filled container encounter conditionswhich result in internal pressures in excess of the 95 psig for whichthey were designed, the containers will gradually and controllablyexpand further. They will not suddenly evert as do the fully orsubstantially fully domed containers of the prior art. This gradualintentional deformation of the bottom wall lessens the risk of explosionand maintains the container in a serviceable condition.

As the container of the present invention expands due to internalpressure. the marginal circular intersection or edge 30 of thedepression or dimple 28 becomes the base upon which the container sits.The stability of the container depends upon the diameter of edge 30 inrelation to the size of the can. The stability of the container isgenerally independent of the extent of its expansion or growth inheight.

Stability of the container is important to the maker and to theconsumer. Unstable cans interfere with the operation of the filling andpacking machinery. Such machinery operates at high speed and cans whichrock or wobble excessively can not be handled by the ma chinery. Fromthe consumers point of view, a can which tips, rocks or wobblesexcessively when set down is an annoyance.

FIG. 12 shows the lower portion of a container according to the presentinvention similar to that of FIG. 6. For convenience, the range of sizesof depressions or dimples is expressed as a percentage ratio of the areaof the dimple to the area of the bottom of the container. The diameter dof the dimple or depression is measured between the centers 41 and 42 ofthe radius 30 which forms the transition or intersection between theexte- -rior surface of the dimple and the exterior surface of theannular panel 26 of the bottom. Similarly. the diameter D of the bottomis measured between the centers 43 and 44 of the radius 320 which formsthe transition between the outer diameter of the annular panel 26 andthe side wall 22. The ratio of the squares of these diameters (d /D isequal to the percentage area ratio. This manner of measurementrealistically determines the relative areas upon which pressure acts todeform the container and eliminates the relatively rigid sidewalltransition angle 32 or radius 32a. FIG. 7 shows the centers to be usedfor measurement of a bevelled or angled transition style of bottom usingthe same numbers as are used in FIG. 12. By way of example, a 1% inchnominal dimple diameter in a 210 (2 10/16 inch) diameter beer can havinga radiused transition bottom as i1- lustrated in FIG. 12 has an arearatio of 41.4 percent. The measured bottom diameter D between transitionradii centers is 2.291 inch and the measured dimple diameter d betweentransition radii centers is 1.474 inch.

Referring again to FIGS. 1, 2, 5 and 6, it has been found that the areaof the base of the depression 28 must be between approximately 15percent and percent of the total area of bottom wall 24 in order toprevent the inward curvature of depression 28 from bulging outward underincreased pressures.

DESCRIPTION OF A PREFERRED EMBODIMENT A can according to one preferredembodiment is a 210 size l2-ounce can suitable for beer or carbonatedbeverages according to FIG. 2. It is made by drawing and ironing 103 lb.Tl tin electroplated steel plate about 0.01 1 inch thick. The nominaloutside diameter of the can body is 2 10/16 inch. The actual outsidediameter is 2.556 inch. The actual height measured from the flat annulus26 to the top of the lid flange 34 is 4.812 inch. The sidewalls are0.0038 inch thick. The bottom wall is joined to the cylindrical sidewallby a transition radius of 0. 125 inch to the inside. The diameter d ofthe dimple or depression measured to the centers of the transition radiiis 1.475 inch for a nominal dimple diameter of 1.375. The dimple isapproximately eliptical in section in that it is generated by a majorradius of 1.500 and minor radii of 0.250. The dimple edge transitionradius between the annular panel and the dimple is 0.050 to the inside.Angle A between the dimple and the annular panel is approximately Thearea ratio of dimple area to bottom area is 41.1 percent.

A can according to a second preferred embodiment is also a 2l0 sizel2-ounce pressurized beverage can according to FIG. 2. It is made bydrawing and ironing 0.014 inch 3004 I-I-l9 aluminum. The dimensions areidentical to those of the steel can described above with the exceptionsof an actual outside diameter of 2.559 inch, a sidewall thickness of0.0048 inch, a dimple edge transition radius of 0.055 inch and a dimplediameter d of 1.485 inch for a nominal dimple diameter of 1.375 inch.The ratio of dimple area to bottom area is about 41.7 percent.

TEST RESULTS Comparison tests of the deformations encountered with aflat bottom wall container, a full concave bottom wall container asdepicted in FIG. 3, and a container according to the present inventionwere made. The 12- ounce containers utilized in these tests were drawnand ironed from the same material, i.e. 0.013 inch, type L steel havinga Rockwell Hardness of R 30 T scale 53:3 and a number 50 electrolytictin plate. This material is called 1 l8 pound plate. The dimensions ofthe tested containers were nominally 2 1 1/16 inches in diameter andnominally 4 13/16 inches in height. The container constructed accordingto the present invention (Table III) was provided with a 45 angledtransition edge, a depression having the shape of a segment Ofa sphereof 1 inch radius and a height of approximately 0.260

inches. a nominal diameter of L25 inches, and an area ratio of 37.3%.The following tables compare measured deformations of the various bottomwall configurations at stated pressures:

TABLE I 5 stability of the container when it positioned in the uprightstanding position. In addition to the above de- End Ang'ed gl f'gsscribed container which is the l2-ounce size, other dif- Press ngDerurmamm Datamation s im fcrently dimensioned containers have beenproduced W s (Immune Ccmcflim Cmmwmfi and studied with similarlysatisfactory results. One such (l gmhle m container, having a lO-ouncecapacity. was constructed Unmhlc with a 2 15/32 inch nominal diameterand a nominal 60 .057 .037 Unstable h 80 047 Unsmhc eight of 4 13/ 16Inches. The depression in the bottom \00 .080 .057 Unstable wall of thiscontainer was identical to the depression in the bottom wall of thetwelve ounce container of Table 15 Ill. A 32-0unce container has alsobeen constructed with nominal sizes of 3 7/16 inch diameter and 6 1 1/16TABLE II Full Concave Bottom Wall Perma- Perma- "611 nent Defurma-Del'orma- Del'orma- Deformation at tion at tion at tion at Depres-Deprcsedge of edge of Pressure sion sion Depres- Depres Stability (psigjCenter Center sion sion Comments 0 0 0 0 0 Stable 40 .005 .001 .002.0005 Stable 00 .010 .003 .005 .002 Stable s0 .02i .010 .01 l .007 semiss CATASTROPHIC FAILURE AT THIS PRESSURE Untittlhiu TABLE III Bottom WallAccording to Present Invention Perma- Permanent nent Dcforma- Dcforma-Dcfurma- Deformation at tion at tion at tion at Depres- Depresedge ofedge of Pressure sion sion Depres- Dcpres- Stability (psig) CenterCenter sion sion Comments 0 U (I U (I Stable 40 ms .021 022 .008 Stable60 0M .04 l 5 .044 .020 Stable $0 .080 .007 .004 .049 Stable I00 .120100 .085 .0745 Stabic l .150 .lZh .|05 .095 Stable The results of thesetests indicate first of all that the container having the flat bottomwall was unstable in inch height. The bottom wall depression had a basedithe upright standing position due to bulging of the cenameter ofapproximately L66 inches and a height of ter portion of the bottom wallat pressures over approxapproximately 0.44 inches and the shape of asegment imately psig, thereby making it totally unsuitable for of asphere of one inch radius. pressurized products such as beer andcarbonated bev- Data from extensive testing of cans made in accorerages.The full concave bottom wall construction dance with the presentinvention are graphically disdemonstrated a catastrophic failure. inother words a played in FIGS. 13 through 21. FIGS. 13-16 each showsudden eversion. popping out or bulging of the bottom can height growthin inches plotted against internal wall. at pressures beyond 80 psig.However, at low pressure for various diameter dimples or depressions.pressures the deformation at the center of the full con- FIG. 17 is aplot of tilt angles for various nominal dimcave depression wassubstantially smaller, as indicated plc diameters. FIGS. 18-21 show thepercentage in the tables, than in the case of the other construcchangein dimple depth measured from rim 30 to the tions. The depression in thebottom wall of the concenter of the dimple plotted against internalpressures tainer of the present invention was found to remain in forvarious nominal dimple diameters. the inward direction without anysubstantial reduction To generate the data of FIGS. l32i, cans were inits cross-sectional area up to 110 psig. in addition made of aluminumand of steel in two thicknesses for stability tests indicated no rockingwith the containers each material. The cans were formed by the drawingof the present invention and they were rated stablc at and ironingprocess. The thicker materials represent all pressures specified. thecurrent commercial minimum thicknesses for con- As can be readily seenfrom studying the above tables, an internally pressurized containerconstructed in accordance with the present invention is able to maintainits stability in the upright standing position at 8 higher pressuresthan similar prior art containers. Furthcrmore, the thickness andstrength of the bottom wall material may be diminished, relative to theother constructions. without correspondingly diminishing the vcntionalfully domed bottom pressurized beverage cans. The thinner materialsrepresent the minimum thickness for pressurized beverage cans nowpossible when made in accordance with the present invention.

All cans were made with a nominal outside diameter of 2 /16 inch. Thisis a common lZ-ouncc size for beer or carbonated beverages and isfrequently called a 210 can. The cans were made with spherical dimpleswhich range from 0.750 inch to 1.852 inch in nominal diameter. Angle Abetween the dimple and the flat annulus was 43 for all cans. The steelcans were made from 1 l 8 pound and 103 pound tin electroplate stockofTl temper having respective thicknesses of 0.013 inch and 0.0! 1 inch.The sidewall thickness of the finished can bodies was 0.0038 inch. Thealuminum cans were made from 0.017 inch and 0.014 inch 3004 l-I-l9drawing and ironing alloy and had a wall thickness of 0.0048 inch. Thetransition radius between the sidewall and the flat annulus of thebottom was approximately 0.125 inch.

The can bodies were subjected to internal air pressure in a testingfixture which permitted measuring the increase in height of the can atdifferent pressures. The cans were subjected to increasing pressures upto l 10 psi or until the can failed or obviously would hold no morepressure. Each height growth reading for an increased pressure was madeat that increased pressure, but was preceded by a return to 30 psi in aneffort to simulate the pressure cycling which a can filled withpressurized beverage might be expected to encounter in commerce. Heightdata for five identical cans was collected and the average of the fivewas plotted as a function of pressure. The curves of FIGS. l3-l6 arefitted to those five-can average data points for each dimple size. Thus.dimple size is the parameter for the graphs.

The following tabulation relates nominal dimple diameters to the letterkey used in FIGS. 13-16 and 18-21 to identify the curves and alsorelates nominal dimple diameter to the ratio of the dimple area to thebottom area as measured in the manner described in connection with FIG.12:

Comparison of FIGS. 13 through l6 shows that larger diameter dimplesinitially resist height expansion more than the smaller dimples. At ahigher pressure the curves for the larger dimples increase in slope andcross over the curves for the smaller dimples. This indicates that therate of height growth for the larger dimples rather suddenly exceeds therate of height growth for the smaller dimples. Soon after thiscross-over, the larger dimple cans either fail or diplay a very greatrate of height growth indicating imminent failure. The actual increasein height is not particularly significant so long as it is notexcessive. The can filling and handling machinery can be adjusted toaccommodate high cans. A height increase of much more than one-quarterinch in a 12 ounce container would be excessive. Of more significance isthe slope of the curve which represents the rate of increase in height.The steep slope typical of the larger dimples means a large change inheight for a small change in pressure. This indicates that the can is 10near failure and also indicates that there will be noticeabledifferences in height among neighboring cans. Wide height variationsamong cans will lead to machine handling difficulties and is anaesthetic problem.

FIGS. 18-21 show the percentage ratio of the change in dimple depth tothe original dimple depth. The data for these Figures was derived alongwith the can height growth data of FIGS. 13-16 from the same cans undertest. Comparison of FIGS. 18-21 reveals that the larger diameter dimplesabove a percent area ratio tended to roll out or flatten severely atpressures well below 95 psig.

As was stated before, 95 psig is taken to be the practical minimumpressure capability for pressurized product cans intended for beer andhighly carbonated beverages. Consequently, cans which display a highrate of increase in height growth or dimple flattening or rollout atpressures below 95 psig are not acceptable.

It is clear from FIGS. 13 through 16 and 18 through 2] that curves A andB represent cans that failed below 95 psig or in the case of0.0l 7aluminum represent cans with height growth rates or dimple depth changerates which are unacceptable before 95 psig is reached. Curve A is forcans having a nominal dimple diameter of 1.852 inches or an area ratioof 72.5 percent. Curve B is for cans having a nominal dimple diameter of1.750 or an area ratio of 65.1 percent. Curves C through G representcans which have nominal dimple diameters of 1.500 inches or less. Thesecans display acceptable height growth and dimple depth changecharacteristics. Translated into 'area ratios. cans above about 60percent are unacceptable.

It should be noted that the data for the curves of FIGS. 13 through 16represent can height growth at a particular pressure. The can willcontract in height if the internal pressure decreases, but will notnecessarily return to the height which that lower pressure would havecaused initially because some permanent deformation occurs. By way ofillustration, an aluminum beer can made from 0.0l4 stock with a nominal1.375 inch dimple is represented by curve D of FIG. 16. At the psiginternal pressure expected during pasteurization, the height growth isslightly more than the 0.125 inch which 85 psig caused. When latercooled, the internal pressure will drop to 30 psig or less. Thepermanent height growth will lie between the 0.050 inch which 30 psigoriginally caused and 0.125 inch, probably on the order of 0.100 inch.Thus, the data of FIGS. 13-16 is not representative of the increase inheight present in .the can when received by the consumer.

FIGS. 13-16 and 18-21 show that smaller dimples better withstandinternal pressures above 60 or more psig.

FIG. 17 shows that stability or resistance to tipping. rocking orwobbling decreases as dimple size is reduced. Although a can with asmall dimple may be excellent from a pressure standpoint. it may beunacceptable from a stability standpoint. The data points plotted onFIG. 17 were obtained by placing filled. sealed and pasteurized l2 ounce210 cans of simulated beer on a horizontal platform and slowly tiltingthe platform until the can started to tip. The angle of the platform andthe nominal dimple size were noted and the average of several cans wasused to produce the data points. Cans having a nominal dimple diameterof 0.750 are considered to be unstable because they rock or wobbledisconcertingly when set upon a table and cause problems 1 1 on highspeed filling and handling equipment. Cans having nominal dimplediameters larger than 0.750 are considered to be adequately stable forprocesscrs and consumers. The larger dimple cans approach the stabil ityof a fully domed bottom can. Translated into area ratios, those canshaving an area ratio above about percent are adequately stable.

As a part of this test program cans of the same description as abovewere made of 90 pound steel plate 0.010 inch thick and of 0.010 inchaluminum. Only a few of the steel cans and none of the aluminum canswere capable of withstanding 95 psig internal pressure. Metal this thinis not appropriate for pressurized beverage cans.

The various testing reported herein verifies that fully domed 210 or 211l2-ounce beer cans are prone to failure at pressures as low as 85 psigunless made of materials stronger than 1 18 pound Tl steel plate or than0.017 inch 3004 H19 aluminum. However, cans according to the presentinvention can be made from 103 pound steel plate or from 0.014 inchaluminum. The enabled use of thinner metal coupled with the smallervolume loss occasioned by the dimple as compared with the full domerepresent very substantial metal savings. Further, the thinner can ofthe present invention is able to withstand the 95 psig pressure requiredfor containers of highly carbonated beverages so that the same can bodycan be used for either beer or beverages at all carbonation levels.Fully domed 0.017 inch aluminum l2-ounce 210 drawn and ironed cans weighapproximately 34 pounds per thousand. Aluminum cans according to thepresent invention are made of 0.014 inch stock and weigh approximately28 pounds per thousand The prior art aluminum cans are over 21 percentheavier. Similarly. fully domed l 18 pound steel 12- ounce 210 drawn andironed cans weigh about 76.9 pounds per thousand whereas 103 pound steelcans according to the present invention weigh about 64.4 pounds perthousand. The prior art steel cans are over 19 percent heavierv Sincemetal is a major factor in can cost, metal savings of this degree aresignificant. Thus, the present invention not only provides a can whichcomfortably withstands significantly higher internal pressures than thefully domed can of the prior art and reduces the chance of explosion ofcans exposed to conditions which generate pressures in excess of thedesign pressure, but also effects a substantial reduction in can cost.

What is claimed is:

1. An eversion resistant, generally cylindrical drawn metal containerhaving therein a product under pres sure, said container including agenerally cylindrical body having integral side and bottom walls, saidbottom wall comprising a central inwardly domed depression surrounded byan annular panel, said depression having a marginal circularintersection with said annular panel, at least said annular panel havingbeen outwardly distended by pressure of said product to permanentlychange the shape of the bottom wall such that said circular intersectionbecomes the outermost extent of the bottom wall, said annular panelbeing inclined into a generally conical shape and forming an obtuseangle with said sidewall. the percentage ratio of the area determined bythe radius of said circular intersec tion to the area determined by theouter radius of said annular panel being in the range of fromapproximately 15 percent to approximately 60 percent, said circular 12intersection alone providing a stable base upon which the containerrests in an upright position.

2. The container of claim 1 wherein the nominal out side diameter of thesidewall is 2 1 1/16 inches, wherein the nominal diameter of thedepression is 1.25 inch, and the container is made from 1 18 poundelectrolytically tin plated steel.

3. The container of claim 1 wherein said depression is concave andremains concave at a pressure of psig.

4. The container of claim 1 wherein the bottom wall comprises 3004 H-l9aluminum and has a thickness greater than 0.010 inch and less than 0.017inch.

5. The container of claim 1 wherein the bottom wall comprises T1 temper,tin-electroplated steel and has a thickness greater than 0.010 and lessthan 0.013 inch.

6. The container of claim 1 wherein the depression is generallyspherical in shape.

7. An eversion resistant, generally cylindrical container drawn frommetal selected from the group consisting of less than 0.013 inch thicksteel and less than 0,017 inch thick aluminum alloy capable ofwithstanding an internal pressure and having therein a product underpressure, said container including a generally cylindrical body havingintegral side and bottom walls, said bottom wall comprising a centralinwardly domed depression surrounded by an annular panel, saiddepression having a marginal circular intersection with said annularpanel, at least said annular panel having been outwardly distended bypressure of said product to permanenlty change the shape of the bottomwall such that said circular intersection becomes the outermost extentof the bottom wall, said annular panel being inclined into a generallyconical shape and forming an obtuse angle with said sidewall, thepercentage ratio of the area determined by the radius of said circularintersection to the area determined by the outer radius of said annularpanel being in the range of from approximately 15 percent t)approximately 60 percent, said circular intersection alone providing astable base upon which the container rests in an upright position.

8. An eversion resistant, generally cylindrical container drawn frommetal selected from the group consisting of less than 0.013 inch thicksteel and less than 0.017 inch thick aluminum alloy capable ofwithstanding an internal pressure of 95 psig and having therein abeverage under pressure, said container including a generallycylindrical body having integral side and bottom walls, said bottom wallcomprising a central inwardly domed depression surrounded by an annularpanel, said depression having a marginal circular intersection with saidannular panel, at least said annular panel having been outwardlydistinded by pressure of said beverage to permanently change the shapeof the bottom wall such that said circular intersection becomes theoutermost extent of the bottom wall, said annular panel being inclinedinto a generally conical shape and forming an obtuse angle with saidsidewall, the percentage ratio of the area determined by the radius ofsaid circular intersection to the area determined by the outer radius ofsaid annular panel being in the range of from approximately 15 percentto approximatcly 60 percent, said circular intersection alone providinga stable base upon which the container rests in an upright position.

9. The container body of claim 8 wherein the percentage ratio of areasis about 50 percent.

10. The container body of claim 8 wherein the percentage ratio of areasis about 40 percent.

11. The container body of claim 8 wherein the percentage ratio of areasis about 35 percent.

12. The container body of claim 8 wherein the per centage ratio of areasis about 30 percent.

13. The container body of claim 8 wherein the per centage ratio of areasis about 25 percent.

14. The container of claim 8 wherein the nominal outside diameter of thesidewall is 2 l/l6 inches and wherein the nominal diameter of thedepression is in the range of from about l inch to about l.5 inches.

15. The container of claim 8 wherein the nominal outside diameter of thesidewall is 2 10/16 inches and the area ratio is about 40 percent.

16. The container of claim 8 wherein the body is a drawn and ironedcontainer body.

17. The container of claim 2 wherein said body comprisestin-electroplated steel.

l8. The container of claim 17 wherein said steel is 103 pound platebefore being drawn and ironed.

19. The container of claim 16 wherein said body comprises aluminum.

20. The container of claim 19 wherein said aluminum is 0.0l4 inch inthickness before being drawn and ironed.

21. An eversion resistant bottom wall construction for a substantiallyrigid drawn metallic cylindrically shaped pressurized beverage containersubjected to internal pressure and having integral side and bottom wallsof thin metal, said bottom wall comprising:

an annular panel integrally connected to the side wall of saidcontainer;

an inwardly extending depression centrally disposed in said panel, saiddepression merging peripherally with said panel in a circular base edge,the supplement of the angle formed therebetween being no less than 43;

the projected area of said depression constituting no less than l5percent and no more than 60% of the total projected area of said bottomwall;

at least said annular panel having been outwardly distended by pressureof said beverage to permanently change the shape of the bottom wall suchthat said circular base edge becomes the outermost extent of the bottomwall, said depression remaining inwardly extending from said annularpanel, said circular base edge alone providing a stable support for saidcontainer.

22. An eversion resistant bottom wall construction for a substantiallyrigid cylindrically shaped beverage container subjected to internalpressure, said bottom wall being of metal selected from the groupconsisting of less than 0.01 3 inch thick steel and less than 0.017 inchthick aluminum alloy, said bottom wall comprising:

an annular panel integrally connected to the side wall of saidcontainer;

an inwardly extending depression centrally disposed in said panel, saiddepression merging peripherally with said panel in a circular base edge;

the projected area of said depression constituting no less than percentand no more than 60 percent of the total projected area of said bottomwall;

at least said annular panel having been outwardly distended by pressureof said beverage to permanently change the shape of the bottom wall suchthat said circular base edge becomes the outermost extent of the bottomwall, said depression remaining inwardly extending from said annularpanel, said cir- 14 cular base edge alone providing a stable support forsaid container.

23. The eversion resistant bottom wall construction for a cylindricallyshaped container as defined in claim 22 wherein the supplement of theangle formed by the peripheral merging of said depression with saidannular flat panel is no less than 43 and no greater than 24. Aneversion resistant, generally cylindrical metal container having thereina product under pressure, said container including a body drawn andironed from relatively thin metal sheet selected from the groupconsisting of less than 0.013 inch thick steel and less than 0.017 inchthick aluminum alloy, said body having a generally cylindrical sidewallhaving a transition edge. said transition edge being integral with abottom wall, said bottom wall comprising a central inwardly concave domesurrounded by an annular panel extending to said transition edge, saiddome having a marginal circular intersection with said panel, at leastsaid annular panel having been outwardly distended by pressure of saidproduct to permanently change the shape of the bottom wall such thatsaid circular intersection becomes the outermost extent of the bottomwall said intersection being in the form of a radius between said domeand said panel, said intersection alone providing a sta ble base uponwhich the container rests in an upright position, the percentage ratioof the area of the circle encompassed by said intersection to the areaof the circle encompassed by the transition edge is in the range of fromabout 15 percent to about 60 percent.

25. The container of cla m 24 wherein the transition edge is an inwardlybevelled section of the sidewall.

26. The container of claim 24 wherein the transition edge is a radius.

27. An eversion resistant bottom wall construction for a substantiallyrigid drawn metallic cylindrically shaped container having therein abeverage under pressure and having integral side and bottom walls ofthin metal, said bottom wall comprising:

an annular panel integrally connected to the side wall of saidcontainer; an inwardly extending depression centrally disposed in saidpanel, said depression merging peripherally with said panel in an angledannular base edge, the angle formed thereby being no less than about 43;

the projected area of said depression constituting no less than 15percent and no more than 60 percent of the total projected area of saidbottom wall;

at least said annular panel having been outwardly distended by pressureof said beverage to permanently change the shape of the bottom wall suchthat said annular base edge becomes the outermost extent of the bottomwall, said depression remaining inwardly extending from said annularpanel, said annular base edge alone providing a stable support for saidcontainer.

28. An eversion resistant bottom wall construction for a substantiallyrigid cylindrically shaped container having therein a beverage underpressure and having integral side and bottom walls drawn and ironed fromsheet metal selected from the group consisting of less than 0.0l3 inchsteel and less than 0.0l7 inch aluminum alloy, said bottom wallcomprising:

an annular panel integrally connected to the side wall of saidcontainer;

an inwardly extending depression centrally disposed in said panel, saiddepression merging peripherally with said panel in an angled annularbase edge, the

16 nular base edge alone providing a stable support for said container.

29. The construction of claim 28 wherein the bottom wall comprises 3004H-l9 aluminum and has a thickness greater than 0.010 inch and less than0.017 inch.

30 The construction of claim 28 wherein the bottom wall comprises T-ltemper, tin-electroplated steel and has a thickness greater than 0.010inch and less than 0.0l3 inch

1. An eversion resistant, generally cylindrical drawn metal container having therein a product under pressure, said container including a generally cylindrical body having integral side and bottom walls, said bottom wall comprising a central inwardly domed depression surrounded by an annular panel, said depression having a marginal circular intersection with said annular panel, at least said annular panel having been outwardly distended by pressure of said product to permanently change the shape of the bottom wall such that said circular intersection becomes the outermost extent of the bottom wall, said annular panel being inclined into a generally conical shape and forming an obtuse angle with said sidewall, the percentage ratio of the area determined by the radius of said circular intersection to the area determined by the outer radius of said annular panel being in the range of from approximately 15 percent to approximately 60 percent, said circular intersection alone providing a stable base upon which the container rests in an upright position.
 2. The container of claim 1 wherein the nominal outside diameter of the sidewall is 2 11/16 inches, wherein the nominal diameter of the depression is 1.25 inch, and the container is made from 118 pound electrolytically tin plated steel.
 3. The container of claim 1 wherein said depression is concave and remains concave at a pressure of 95 psig.
 4. The container of claim 1 wherein the bottom wall comprises 3004 H-19 aluminum and has a tHickness greater than 0.010 inch and less than 0.017 inch.
 5. The container of claim 1 wherein the bottom wall comprises T-1 temper, tin-electroplated steel and has a thickness greater than 0.010 and less than 0.013 inch.
 6. The container of claim 1 wherein the depression is generally spherical in shape.
 7. An eversion resistant, generally cylindrical container drawn from metal selected from the group consisting of less than 0.013 inch thick steel and less than 0.017 inch thick aluminum alloy capable of withstanding an internal pressure and having therein a product under pressure, said container including a generally cylindrical body having integral side and bottom walls, said bottom wall comprising a central inwardly domed depression surrounded by an annular panel, said depression having a marginal circular intersection with said annular panel, at least said annular panel having been outwardly distended by pressure of said product to permanenlty change the shape of the bottom wall such that said circular intersection becomes the outermost extent of the bottom wall, said annular panel being inclined into a generally conical shape and forming an obtuse angle with said sidewall, the percentage ratio of the area determined by the radius of said circular intersection to the area determined by the outer radius of said annular panel being in the range of from approximately 15 percent to approximately 60 percent, said circular intersection alone providing a stable base upon which the container rests in an upright position.
 8. An eversion resistant, generally cylindrical container drawn from metal selected from the group consisting of less than 0.013 inch thick steel and less than 0.017 inch thick aluminum alloy capable of withstanding an internal pressure of 95 psig and having therein a beverage under pressure, said container including a generally cylindrical body having integral side and bottom walls, said bottom wall comprising a central inwardly domed depression surrounded by an annular panel, said depression having a marginal circular intersection with said annular panel, at least said annular panel having been outwardly distinded by pressure of said beverage to permanently change the shape of the bottom wall such that said circular intersection becomes the outermost extent of the bottom wall, said annular panel being inclined into a generally conical shape and forming an obtuse angle with said sidewall, the percentage ratio of the area determined by the radius of said circular intersection to the area determined by the outer radius of said annular panel being in the range of from approximately 15 percent to approximately 60 percent, said circular intersection alone providing a stable base upon which the container rests in an upright position.
 9. The container body of claim 8 wherein the percentage ratio of areas is about 50 percent.
 10. The container body of claim 8 wherein the percentage ratio of areas is about 40 percent.
 11. The container body of claim 8 wherein the percentage ratio of areas is about 35 percent.
 12. The container body of claim 8 wherein the percentage ratio of areas is about 30 percent.
 13. The container body of claim 8 wherein the percentage ratio of areas is about 25 percent.
 14. The container of claim 8 wherein the nominal outside diameter of the sidewall is 2 10/16 inches and wherein the nominal diameter of the depression is in the range of from about 1 inch to about 1.5 inches.
 15. The container of claim 8 wherein the nominal outside diameter of the sidewall is 2 10/16 inches and the area ratio is about 40 percent.
 16. The container of claim 8 wherein the body is a drawn and ironed container body.
 17. The container of claim 2 wherein said body comprises tin-electroplated steel.
 18. The container of claim 17 wherein said steel is 103 pound plate befOre being drawn and ironed.
 19. The container of claim 16 wherein said body comprises aluminum.
 20. The container of claim 19 wherein said aluminum is 0.014 inch in thickness before being drawn and ironed.
 21. An eversion resistant bottom wall construction for a substantially rigid drawn metallic cylindrically shaped pressurized beverage container subjected to internal pressure and having integral side and bottom walls of thin metal, said bottom wall comprising: an annular panel integrally connected to the side wall of said container; an inwardly extending depression centrally disposed in said panel, said depression merging peripherally with said panel in a circular base edge, the supplement of the angle formed therebetween being no less than 43*; the projected area of said depression constituting no less than 15 percent and no more than 60% of the total projected area of said bottom wall; at least said annular panel having been outwardly distended by pressure of said beverage to permanently change the shape of the bottom wall such that said circular base edge becomes the outermost extent of the bottom wall, said depression remaining inwardly extending from said annular panel, said circular base edge alone providing a stable support for said container.
 22. An eversion resistant bottom wall construction for a substantially rigid cylindrically shaped beverage container subjected to internal pressure, said bottom wall being of metal selected from the group consisting of less than 0.013 inch thick steel and less than 0.017 inch thick aluminum alloy, said bottom wall comprising: an annular panel integrally connected to the side wall of said container; an inwardly extending depression centrally disposed in said panel, said depression merging peripherally with said panel in a circular base edge; the projected area of said depression constituting no less than 15 percent and no more than 60 percent of the total projected area of said bottom wall; at least said annular panel having been outwardly distended by pressure of said beverage to permanently change the shape of the bottom wall such that said circular base edge becomes the outermost extent of the bottom wall, said depression remaining inwardly extending from said annular panel, said circular base edge alone providing a stable support for said container.
 23. The eversion resistant bottom wall construction for a cylindrically shaped container as defined in claim 22 wherein the supplement of the angle formed by the peripheral merging of said depression with said annular flat panel is no less than 43* and no greater than 90*.
 24. An eversion resistant, generally cylindrical metal container having therein a product under pressure, said container including a body drawn and ironed from relatively thin metal sheet selected from the group consisting of less than 0.013 inch thick steel and less than 0.017 inch thick aluminum alloy, said body having a generally cylindrical sidewall having a transition edge, said transition edge being integral with a bottom wall, said bottom wall comprising a central inwardly concave dome surrounded by an annular panel extending to said transition edge, said dome having a marginal circular intersection with said panel, at least said annular panel having been outwardly distended by pressure of said product to permanently change the shape of the bottom wall such that said circular intersection becomes the outermost extent of the bottom wall said intersection being in the form of a radius between said dome and said panel, said intersection alone providing a stable base upon which the container rests in an upright position, the percentage ratio of the area of the circle encompassed by said intersection to the area of the circle encompassed by the transition edge is in the range of from about 15 percent to about 60 percent.
 25. The container of claim 24 wherein the transition edge is an inwardly bevelled section of the sidewall.
 26. The container of claim 24 wherein the transition edge is a radius.
 27. An eversion resistant bottom wall construction for a substantially rigid drawn metallic cylindrically shaped container having therein a beverage under pressure and having integral side and bottom walls of thin metal, said bottom wall comprising: an annular panel integrally connected to the side wall of said container; an inwardly extending depression centrally disposed in said panel, said depression merging peripherally with said panel in an angled annular base edge, the angle formed thereby being no less than about 43*; the projected area of said depression constituting no less than 15 percent and no more than 60 percent of the total projected area of said bottom wall; at least said annular panel having been outwardly distended by pressure of said beverage to permanently change the shape of the bottom wall such that said annular base edge becomes the outermost extent of the bottom wall, said depression remaining inwardly extending from said annular panel, said annular base edge alone providing a stable support for said container.
 28. An eversion resistant bottom wall construction for a substantially rigid cylindrically shaped container having therein a beverage under pressure and having integral side and bottom walls drawn and ironed from sheet metal selected from the group consisting of less than 0.013 inch steel and less than 0.017 inch aluminum alloy, said bottom wall comprising: an annular panel integrally connected to the side wall of said container; an inwardly extending depression centrally disposed in said panel, said depression merging peripherally with said panel in an angled annular base edge, the angle formed thereby being about 43*; the projected area of said depression constituting no less than 15 percent and no more than 60 percent of the total projected area of said bottom wall; at least said annular panel having been outwardly distended by pressure of said beverage to permanently change the shape of the bottom wall such that said annular base edge becomes the outermost extent of the bottom wall, said depression remaining inwardly extending from said annular panel, said annular base edge alone providing a stable support for said container.
 29. The construction of claim 28 wherein the bottom wall comprises 3004 H-19 aluminum and has a thickness greater than 0.010 inch and less than 0.017 inch.
 30. The construction of claim 28 wherein the bottom wall comprises T-1 temper, tin-electroplated steel and has a thickness greater than 0.010 inch and less than 0.013 inch. 